Lumber V0.2

local x=0
local y=0
local dir=0
local rows=4
local columns=5
local stop = false

local function forward()
    local moved = true
    while not turtle.forward() do
        if not turtle.dig() and
        not turtle.attack() then
            moved = false
            print("can't move")
            break
        end
    end
    if moved then
        if dir == 0 then
            x=x+1
        elseif dir == 2 then
            x=x-1
        elseif dir == 1 then
            y=y+1
        elseif dir == 3 then
            y=y-1
        else
            print("Unknown dir")
            return false
        end
        return true
    end
    return false
end

local function turnRight()
    turtle.turnRight()
    dir = (dir+1)%4
end

local function turnLeft()
    turtle.turnLeft()
    dir = (dir-1)%4
end

local function cutTree()
    local height = 0
    turtle.dig()
    forward()
    turtle.digDown()
    turtle.select(3)
    while turtle.compareUp() do
        turtle.digUp()
        turtle.up()
        height = height +1
    end
    for i=1, height do
        turtle.down()
    end
end

local function plantTree()
    turtle.suckDown()
    if turtle.getItemCount(2)>1 and not turtle.detectDown() then
        turtle.select(2)
        return turtle.placeDown()
    end
    return false
end

local function detectTree()
    turtle.select(3)
    if turtle.compare() then
        return true
    else
        return false
    end
end

local function move()
    local mod = y%6
    if y==(rows-1)*3 and x==0 then
        stop = true
        print("Stoppinzg")
        return
    elseif (x== columns*3 and mod ==0 and dir == 0) or
        (x== columns*3 and mod == 3 and dir == 1)then
        turnRight()
    elseif (x==0 and mod==3 and dir == 2) or
        (x==0 and mod == 0 and dir == 1)then
        turnLeft()
    else
        if not forward() then
            stop = true
            return
        end
    end

end

local function manageInventory()
    local charcoal, saplings
    local time=0
    local charcoalOk = false
    local saplingsOk = false

    for i=4, 16 do
        turtle.select(i)
        turtle.dropDown()
    end

    turtle.down()

    while not (charcoalOk and saplingsOk) do
        turtle.select(1)
        turtle.refuel(turtle.getItemCount(1)-1)
        charcoal = (200-turtle.getFuelLevel())/96
        saplings = (rows*columns)-turtle.getItemCount(2)
        if charcoal > 0 then
            print("Waiting for "..charcoal.." charcoal")
            redstone.setOutput("left", true)
            time = charcoal
        else
            time=0
            redstone.setOutput("left", false)
            charcoalOk = true
        end
        if saplings > 0 then
            print("Waiting for "..saplings.." saplings")
            redstone.setOutput("right", true)
            if time > saplings or time == 0 then
                time = saplings
            end
        else
            redstone.setOutput("right", false)
            saplingsOk = true
        end

        os.sleep(time*2.5)
    end

    redstone.setOutput("left", false)
    redstone.setOutput("right", false)
    if(time>0) then
        os.sleep(10)
    end
    turtle.up()
end

local function returnHome()
    turnRight()
    for i=1,y do
        while not turtle.forward() do
            turtle.attack()
        end
    end
    x=0
    y=0
    dir=0
    turnRight()
end

local function mainLoop()
    while true do
        manageInventory()
        while not stop do
            move()
            if detectTree() then
                cutTree()
            end
            plantTree()
        end
        returnHome()
        print("finished")
        os.sleep(120)
    end
end

mainLoop()